1. Field of the Invention
The invention relates generally to an indicator system for remotely sensing and indicating first, second and third status conditions of a three state element. More particularly, the invention relates to a remote switch position scanner and display system for scanning remotely located switches which are responsive to a multi-state element such as a valve or the like wherein the position of the switches are sensed and displayed at a central location. The switches may be not only responsive to an operating element such as a valve but also may be responsive to tripped or closed circuit breakers, out of limit condition indicators, and the like.
2. Description of the Prior Art
In prior art remote scanning and indicating systems, the number of electrical conductors has equaled the number of switches to be scanned and sensed plus at least one common conductor. These prior art systems are disadvantageously expensive when large numbers of elements are to be remotely scanned because a large number of conductors have been required for the long cable runs.
The prior art systems also have lighted indicator lamps at the central location with the interrogating signal. Where extremely long conductor runs exist between the remote location and the central control location, the inductance of the conductors has required that the frequency of interrogatory signals be low with the result that the lamp or other indicators flicker in response to the low frequency driving the lamp.
Thus, it is an object of the invention to provide a new and improved remote scanning and indicating system which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a remote scanning and indicating system requiring but two conductors per element to be sensed.
It is a further object of the invention to provide control electronics for the remote scanning and indicating system which stores the status of the switches to be sensed and control indicator lamps driven by a sixty cycle source by opening or completing one or more closed lamp circuits.